Romain Grosjean says the struggles faced by Haas at the Mexican Grand Prix are "a slap in the face" for the team after being slowest in qualifying.

While Pierre Gasly didn't take part in Q1 on Saturday, Grosjean was the slowest of those to set a time in the first part of qualifying, ending up 0.03s slower than teammate Kevin Magnussen. With both Haas cars being beaten by the two Saubers – running a year-old Ferrari power unit – Grosjean says the difficulties in Mexico highlight the need for Haas to understand its car better.

"We're not super-good on the tire usage but I don't think that's the biggest problem," Grosjean said. "We've got two setups that are pretty different between the cars and we haven't got one that is outstandingly good compared to the other one. I think it's a bit of a slap in the face and a wake-up call – we need to get our heads down and try to understand why we're slipping away through the season.

"We know how much more horsepower we've got compared to Sauber and they are in front of us, so that shows we need to do things better.

"[Sauber] were far away initially and they've come back pretty well, so they must have got something right. I don't think we went backwards, I think we're pretty much stable. We know a track like this or Singapore where we need extra downforce we are not good because we don't get the extra downforce. It's no excuse, because we didn't have it last year so we haven't reacted well.

"It's a lot of things that are easy to say right now with two years of experience, but from next year I think we need to engage second gear and say, 'Look guys, now is the time we push ourselves high up.'"

Agreeing with Grosjean's assessment, team principal Guenther Steiner says the team's weakness is a lack of performance when running high downforce.

"It's just a bad weekend," Steiner said. "You're very conscious of something like this happening when we started as our high-downforce setup is not ideal to say the least, to be complementary. We need to work on it. I don't want to talk or find excuses – there is no excuse. We did not just do a good enough job on it... end of story."